Central tire inflation system and method

ABSTRACT

A central tire inflation system for a tire. The system includes one or more pneumatic control valves for controlling inflation of a respective tire. A first compressed air source is provided for supplying compressed air to inflate the tire. A second compressed air source is provided for supplying compressed air to control the at one or more pneumatic control valves. A control means is provided for controlling the supply of compressed air from the second compressed air source to generate a pneumatic control signal to control the one or more pneumatic control valves. The first compressed air source can be a compressor configured to provide compressed air to inflate the tires. The second compressed air source can form part of an air suspension system.

TECHNICAL FIELD

The present invention relates to a central tire inflation system (CTIS)and to a related method. The present invention also relates to aprocessor for controlling operation of a central tire inflation system(CTIS) to inflate at least one tire of a vehicle and to a relatedmethod. The present invention also relates to an electronic control unit(ECU); to a vehicle; and to related computer program products.

BACKGROUND

Central tire inflation systems (CTISs) were originally developed formilitary applications, in particular for military applicationsconcerning off-road military wheeled trucks and trailers. However, CTISsare nowadays incorporated into non-military vehicles such as specialistconstruction equipment and some agricultural vehicles.

A CTIS typically comprises a compressed air source located on-board thevehicle and connected to one or more tires. Tire pressure can thereforebe adjusted by operating the CTIS. The CTIS delivers compressed air totire supply lines. In some examples, the supply lines are integratedinto the vehicle axles. Various valves are provided in the CTIS tocontrol flow of compressed air.

At least in certain embodiments, the present invention aims to solve, orat least mitigate, at least some problems that can be identified in theprior art, and/or to provide an improved CTIS and/or CTIS controlstrategy compared to the prior art.

SUMMARY OF THE INVENTION

Aspects of the present invention relate to a CTIS; to a vehicle; to arelated method; and to a related computer program product. Aspects ofthe present invention also relate to a processor; to an ECU; to a CTIS;to a vehicle; to a related method; and to a related computer programproduct.

According to an aspect of the present invention, there is provided acentral tire inflation system for a vehicle comprising:

at least one pneumatic control valve for controlling inflation of arespective tire;

a first compressed air source for supplying compressed air to inflatethe tire;

a second compressed air source for supplying compressed air to controlsaid at least one pneumatic control valve; and

control means for controlling the supply of compressed air from thesecond compressed air source to generate a pneumatic control signal tocontrol said at least one pneumatic control valve.

At least in certain embodiments, the first and second compressed airsources can have different operating parameters suitable for performingthe respective functions of inflating the tire(s) and generating thepneumatic control signal. The second compressed air source can operateat a higher pressure than the first compressed air source. The at leastone pneumatic control valve can have a higher activation pressure thanthe operating pressure of the first compressed air source. Thus, atleast in certain embodiments, the operation of the first compressed airsource will not interfere with operation of the at least one pneumaticcontrol valve. Moreover, the first compressed air source can have ahigher flow rate than the second compressed air source suitable forinflating the tire.

The pneumatic control valve is operable to change state in response tothe pneumatic control signals. The pneumatic control signal comprisesfluid pressure changes in a control line in communication with thepneumatic control valve. The first compressed air source can optionallyalso be connected to the control line. Thus, the control line canfunction as a supply line for supplying compressed air from the firstand second compressed air sources to the tire. The pneumatic controlvalve can be disposed in said supply line. The pneumatic control valvecan cycle between different states in dependence on said pneumaticcontrol signal. For example, the pneumatic control valve can cyclebetween one or more of the following: a closed state (for normalrunning), an open state (for inflation), and a deflation/pressuremeasuring state. The first compressed air source can provide asubstantially steady state supply of compressed air for inflating thetire. The second compressed air source can supply a control signal forcontrolling operation of the pneumatic control valve. The control signalcan be a pneumatic control signal for controlling operation of thepneumatic control valve.

The first compressed air source can be distinct and/or separate from thesecond compressed air source, or may be connected. For example the firstand second air sources may each comprise a dedicated compressor, or asingle compressor could be used in combination with one or morereservoir vessels to provide the second air source. The first and secondcompressed air sources can each be in fluid communication with one ormore compressed air supply lines. The first compressed air source can,for example, consist of a dedicated compressor without an associatedreservoir such that air is supplied directly from the compressor to thetires of the vehicle, via associated valves.

The second compressed air source can comprise a reservoir operating at ahigher pressure than the supply of air from the first compressed airsource for inflating the tires of the vehicle. The use of a reservoir inthe second compressed air source is advantageous as it is not necessaryperiodically to operate a compressor to generate the pneumatic controlsignal which would require additional compressor cycles, contributing tocompressor deterioration over time. The second compressed air source canbe configured to deliver compressed air at a lower pressure than thereservoir pressure, at or above a minimum activation pressure requiredto switch the pneumatic control valve, by means of a pressure reductionvalve at the reservoir outlet. The switching pressure may be regulatedto approximately 5 bar.

The vehicle can have more than one tire. For example, the vehicle canhave four tires; two front tires mounted on a front axle and two reartires mounted on a rear axle. The CTIS can be configured to inflate oneor more tires at a time. In particular, the CTIS can be configured tosimultaneously inflate all of the tires of the vehicle, or tosimultaneously inflate two or more tires connected to a same axle of thevehicle. The inflation of each tire can be controlled by a respectivepneumatic control valve. However, a pneumatic control valve couldsimultaneously control the supply of compressed air to two or moretires.

A staggered tire inflation strategy can be implemented to inflate thetires on each axle in sequence. The tires on the front axle could beinflated before the tires on the rear axle. Alternatively, the tires onthe rear axle can be inflated before the tires on the front axle. Atleast in certain embodiments, the latter approach can help to preservethe dynamic stability or handling balance of the vehicle. In particular,by inflating the tires mounted to the rear axle and then inflating thetires mounted to the front axle the handling characteristics of thevehicle can, for example, be biased towards understeer. This approach isadvantageous if the CTIS is to operate when the vehicle is moving.

The first compressed air source can be a first compressor associatedwith the CTIS. The first compressor can be a dedicated compressor forinflating one or more tires. The first compressed air source can be ahigh-flow compressed air source configured to deliver a higher flow ratethan the second compressed air source. The second compressed air sourcecan be a low-flow compressed air source configured to deliver a lowerflow rate than the first compressed air source. The first compressed airsource can be configured to deliver air at a high flow rate and a lowpressure (HF/LP) to the tires of the vehicle. The second compressed airsource can be configured to deliver air at a low flow rate and a highpressure (LF/HP). The characteristics of the air delivered by each ofsaid first and second air sources can be controlled by respective flowcontrol devices, such as a flow regulator.

The terms “high” and “low” are used herein as relative terms to definethe characteristics of the air delivered by the first and secondcompressed air sources. The first compressed air source can beconfigured to deliver air at a lower pressure than the second compressedair source. Equally, the first compressed air source can be configuredto deliver air at a higher flow rate than the second compressed airsource. It will be appreciated that references herein to the delivery oflow pressure air occurs at a pressure above the tire pressure in orderto perform the required tire inflation function.

The dedicated compressor of the first air supply can be powered by anelectric motor or from the vehicle engine. The dedicated compressor candeliver air at a maximum pressure output of at least 5 bar, preferablyin the range of 5 to 12 bar, more preferably in the range of 8 to 10bar.

The CTIS can comprise a valve block. The valve block can be configuredfor receiving incoming compressed air supplied by the first and/orsecond compressed air sources. The valve block can be configured todistribute said compressed air to the one or more tires, as required.The valve block can comprise one or more inlet valves, each forcontrolling flow of compressed air from a respective one of the firstand second compressed air sources. The one or more inlet valves cancontrol the supply of compressed air into a gallery provided in saidvalve block. A first inlet valve can be provided for controlling flow ofcompressed air from the first compressed air source. A second inletvalve can be provided for controlling flow of compressed air from thesecond compressed air source. The second inlet valve can function as theflow control means for generating the pneumatic control signals. Thevalve block can comprise one or more outlet valves, each for controllingflow of compressed air from the valve block to one or more of the tiresof the vehicle. Each tire can have an associated outlet valve. Each tirecan have an associated tire supply line extending from the valve blockto the corresponding pneumatic control valve. The tire supply lines canbe in fluid communication with said one or more compressed air supplylines via the valve block.

The control means is provided for controlling the supply of compressedair from the second compressed air source to generate said pneumaticcontrol signal. The flow control means can comprise one or more of saidinlet valves and/or one or more of said outlet valves. The one or morevalves can each be an electromechanical valve, for example a solenoidvalve. The valve can be an inlet valve for controlling the supply ofcompressed air from the second compressed air source to the valve block.The compressed air from the second compressed air source can be suppliedto a gallery in the valve block. The valve can control the supply ofcompressed air into said gallery. The outlet valve can control thesupply of compressed air from the gallery into one or more of said tiresupply lines.

In use, the control means generates a pneumatic control signal tocontrol said pneumatic control valve(s). In systems comprising aplurality of pneumatic control valves, the control means can beconfigured to control each pneumatic control valve independently.Alternatively, or in addition, the control means can be configured togenerate a pneumatic control signal to control more than one of saidplurality of pneumatic control valves simultaneously. In certainarrangements, the control means can be configured to generate apneumatic control signal to control all of said plurality of pneumaticcontrol valves simultaneously. The central tire inflation system cancomprise a separate valve associated with each tire supply line tocontrol the communication of the pneumatic control signal to thepneumatic control valve associated with that tire supply line. Forexample, the outlet valves of the valve block could be operatedselectively to deliver the pneumatic control signal only to those tirelines containing a pneumatic control valve which is to be controlled.

Each tire supply line can be operative to supply compressed air fromsaid first compressed air source and/or from said second compressed airsource. In use, compressed air can be supplied to the tire supply lineeither from the first compressed air source or from the secondcompressed air source. Alternatively, compressed air can be suppliedfrom both the first and second compressed air sources simultaneously.

The pneumatic control valve has a plurality of operating states. Thepneumatic control valve can toggle between said operating states, orcycle through said operating states in dependence on the pneumaticcontrol signal. For example, upon receipt of a pneumatic control signal,the pneumatic control valve can toggle to another operating state, orcan cycle to the next operating state in a sequence. The pneumaticcontrol signal can, for example, comprise a pulse of high pressure air.

An electronic control unit (ECU) can be provided to control operation ofthe CTIS. The ECU can control the first compressed air source and/or thesecond compressed air source. In addition, or alternatively, the ECU canbe configured to control the valve block. The ECU can control theoperation of said first inlet valve, said second inlet valve and said atleast one outlet valve to control the supply of compressed air to the oreach tire supply line. It will be understood that control by the ECU ofthe first and/or second compressed air source, dedicated compressor,valve block and/or any other component of the CTIS as described herein,is by generation of one or more signals which can be routed anddelivered as appropriate by a vehicle communication network. The vehiclecommunication network can be part of a vehicle control system. Thevehicle communication network can comprise a controller area network(CAN). The vehicle control system can comprise said ECU.

The CTIS can comprise an air dryer unit for drying compressed airsupplied by said first compressed air source and/or said secondcompressed air source. The valve block can control the supply of air tothe air dryer unit. The ECU can control a purge function of the airdryer unit. For example, the ECU can control the valve block to exhaustair through the air dryer unit to expel collected water. The ECU caninitiate a purge cycle when the air dryer unit has reached a predefinedsaturation threshold.

In one arrangement the second compressed air source can be a compressedair source associated with the air suspension system for controlling thevehicle suspension. The second compressed air source can be an airsuspension reservoir. The air suspension system can comprise acompressor, an air suspension reservoir, and one or more pneumaticactuators. At least in certain embodiments, the one or more pneumaticactuators can control the operating characteristics of the vehiclesuspension, for example to adjust the ride height of the vehicle. Thecompressor can charge the reservoir with air at a pressure up to 25 bar,preferably in the region of 12 to 20 bar. In one embodiment thereservoir may be charged up to a pressure of 16 bar. A pressureregulator is preferably provided between the second compressed airsource and the pneumatic control valve to reduce the air pressure towithin a working pressure range of the pneumatic control valve. Usingthe air suspension reservoir to function as the second compressed airsource is advantageous since the relatively low volumes of high pressureair required to generate the pneumatic control signal can be taken fromthe air suspension reservoir without affecting the vehicle ride heightor vehicle stability, and avoids the need for a further reservoir and/orreservoir.

In an alternative arrangement the first compressed air source cancomprise a first compressor. In a first operating mode, the firstcompressor can supply air directly to the tires of the vehicle, withoutpassing through any intervening reservoir. The first compressor can alsobe selectively connected to a reservoir associated with the secondcompressed air source. The compressor can be operated to charge saidreservoir. In use, the reservoir can be charged to a pressuresignificantly above the tire pressure, for example, for a tire pressurein the range of 1.5 to 3 bar the reservoir pressure of the second airsupply may be in the range of 5 to 10 bar, or greater. Advantageously,by providing the second compressed air source at a higher pressure, eachpulse of air provided therefrom to operate the pneumatic control valvecan result in a small change in the reservoir pressure. In this mannerit may not be required to run the compressor each time the pneumaticcontrol valves are operated, thereby reducing compressor cycling andpotentially increasing compressor life. Once the reservoir pressurefalls below a lower threshold, providing the compressor is not supplyingair to the tires of the vehicle, the first compressor can be operated torecharge the reservoir. For example, one or more control valvescontrolling the flow of air from the compressor may be configured todirect air from the compressor to the reservoir. Alternatively, wheneverthe compressor is run, prior to shutting off the compressor thereservoir can be recharged, thereby maintaining the reservoir in acharged condition without increasing the on/off cycles of thecompressor. For example, the one or more control valves can be operatedto switch from providing a fluid connection between the compressor andsaid tire(s) to establishing a fluid connection between the compressorand said reservoir.

The valve block can comprise a gallery. The first compressed air sourceand/or the second compressed air source can be in selective fluidcommunication with said gallery. The valve block can comprise a firstinlet valve for controlling the flow of compressed air from the firstcompressed air source to the gallery. The valve block can comprise asecond inlet valve for controlling flow of compressed air from thesecond compressed air source to the gallery.

An outlet valve can be provided to control the supply of compressed airto each tire supply line. In an embodiment, the valve block can havefour outlet valves, each connected to a respective one of four tiresupply lines, each for supplying compressed air to a respective one offour tires. The four tires can be a front left, front right, rear leftand rear right tire of an vehicle.

Although described herein in respect to inflation of wheels on two axlesof a vehicle, in another embodiment the CTIS may supply pressure only totires on the driven axle of the vehicle. In such an embodiment the valveblock can have two outlet valves, each connected to a respective one oftwo tire supply lines, each for supplying compressed air to a respectiveone of two tires disposed on the driven axle of a two wheel drivevehicle. The two tires may be a front left and front right tire (frontwheel drive) or may be a rear left and rear right tire (rear wheeldrive).

The valve block can comprise one or more exhaust valves for exhaustingcompressed air from the valve block to atmosphere.

The inlet valve(s) and/or the outlet valve(s) and/or the exhaustvalve(s) can each be a solenoid valve. A solenoid valve can be anormally-closed type valve. A solenoid valve can be a normally-open typevalve. The valve block can also comprise a safety valve. The safetyvalve can be a solenoid, normally-open type valve.

Each pneumatic control valve can be operably coupled to a respective oneof the tire supply lines of the vehicle. The pneumatic control valve canbe mounted to a wheel, optionally removably. In an arrangement, thepneumatic control valve can be a latching valve. The pneumatic controlvalve can cycle between one or more of the following: a closed state(for normal running), an open state (for inflation), and adeflation/pressure measuring state. The pneumatic control valve cancycle between said states in dependence on the control signal suppliedby the second compressed air source.

The ECU can control operation of one or more of the following: the firstinlet valve; the second inlet valve; the outlet valve(s); the exhaustvalve(s); and/or the safety valve(s).

According to another aspect of the present invention, there is provideda method of operating a CTIS to inflate a tire of a vehicle, the methodcomprising the steps of:

using a first compressed air source, providing a first supply ofcompressed air for inflating the tire;

using a second compressed air source, generating a pneumatic controlsignal to control operation of a pneumatic control valve for controllinginflation of the tire.

According to another aspect of the present invention, there is providedan ECU for controlling a CTIS, the ECU comprising a processor asdescribed herein.

According to another aspect of the present invention, there is provideda CTIS comprising a processor as described herein, or an ECU asdescribed herein.

According to another aspect of the present invention, there is provideda vehicle comprising a CTIS as described herein.

According to another aspect of the present invention, there is provideda computer program product comprising a computer readable storage mediumincluding computer readable program code, wherein the computer readableprogram code when executed causes a CTIS to implement a method asdescribed herein.

As used throughout the application, the singular form of “a”, “an” and“the” may include plural referents unless the context clearly dictatesotherwise.

For the avoidance of doubt, references herein to a central tireinflation system (CTIS) are to an apparatus for controlling the pressureof one or more tires.

Within the scope of this application it is expressly intended that thevarious aspects, embodiments, examples and alternatives set out in thepreceding paragraphs, in the claims and/or in the following descriptionand drawings, and in particular the individual features thereof, may betaken independently or in any combination. Features described inconnection with one embodiment are applicable to all embodiments, unlesssuch features are incompatible.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the present invention will now be described,by way of example only, with reference to the accompanying Figures, inwhich:

FIG. 1A is a schematic representation of a central tire inflation system(CTIS) according to an embodiment of the invention;

FIG. 1B is a schematic representation of a valve arrangement of the CTISshown in FIG. 1A;

FIG. 1C is a vehicle system boundary diagram representing the CTIS shownin FIGS. 1A and 1B;

FIG. 2 is a high level block diagram illustrating the operation of theCTIS described herein;

FIG. 3 is a block diagram illustrating a target tire pressure settingstrategy implemented by the CTIS described herein;

FIG. 4 is a block diagram illustrating a target tire pressuremaintaining strategy implemented by the CTIS described herein;

FIG. 5 is a block diagram illustrating in detail a tire deflationstrategy implemented by the CTIS described herein;

FIG. 6 is a block diagram illustrating in detail a tire inflationstrategy implemented by the CTIS described herein;

FIG. 7 is a block diagram illustrating in detail an alternative tiredeflation strategy implemented by the CTIS described herein;

FIG. 8 is a table showing the status of the valves of the CTIS describedherein through a tire deflation cycle involving simultaneous deflationof all four tires;

FIG. 9 is a table showing the status of the valves of the CTIS describedherein through a tire deflation cycle involving one tire at a time;

FIG. 10 is a table showing the status of the valves of the CTISdescribed herein through a tire inflation cycle which switches the tirepressures from those relating to an off road driving mode to thoserelating to an on road driving mode;

FIG. 11 is a table showing the status of the valves of the CTISdescribed herein through a tire inflation cycle involving one tire at atime;

FIG. 12 is a table showing an estimated annual valve usage for thevalves of the CTIS described herein;

FIG. 13 is a series of graphs showing: a) the pressure measured by atire pressure monitoring sensor; and b) the status (open=1; closed=0) ofthe valves of the CTIS described herein, through part of a tiredeflation cycle concerning the rear axle;

FIG. 14 is a series of graphs showing: a) the pressure measured by atire pressure monitoring sensor; and b) the status (open=1; closed=0) ofthe valves of the CTIS described herein, through another part of thetire deflation cycle referred to in FIG. 13;

FIG. 15 is a group of graphs showing: a) the pressure measured by a tirepressure monitoring sensor; and b) the status (open=1; closed=0) of thevalves of the CTIS described herein, through part of a tire inflationcycle concerning the rear axle; and

FIG. 16 is a group of graphs showing: a) the pressure measured by a tirepressure monitoring sensor; and b) the status (open=1; closed=0) of thevalves of the CTIS described herein, through another part of the tireinflation cycle referred to in FIG. 15.

DETAILED DESCRIPTION

In the following description and in the drawings, reference letters areused to collectively or un-specifically identify equivalent oressentially equivalent components. Where necessary, a specific componentin a collection of equivalent or essentially equivalent components isidentified by suffixing a reference letters in subscript format.

A central tire inflation system (CTIS) 1 in accordance with anembodiment of the present invention will now be described with referenceto the accompanying Figures. As shown schematically in FIG. 1A, the CTIS1 is installed in a vehicle VH having four wheels W each having a tire Tmounted on a wheel hub (not shown). The wheels W (and the tires T) areidentified herein based on their relative position on the vehicle VH,namely: front left (FL), front right (FR), rear left (RL) and rear right(RR). This nomenclature is employed to identify the components of theCTIS 1 associated with the respective tires T. The front tires T_(FR),T_(FL) are mounted on a front axle and the rear wheels T_(RR), T_(RL)are mounted on a rear axle of the vehicle.

The CTIS 1 comprises four pneumatic control valves PCV fixedly mountedto the wheel hubs and arranged to control the supply of compressed airto and from a respective tire cavity. The pneumatic control valves PCVare pneumatically operated in response to changes in the pressure in theassociated tire supply line TSL. Specifically, the pneumatic controlvalves PCV are operable to cycle sequentially (i.e. to toggle) betweenan open state and a closed state in response to the application of apressure exceeding a valve activation pressure. The pneumatic controlvalves PCV are stable in both the open and closed state via a latchingmechanism, i.e. they can each be considered as a pressure actuatedbi-stable valve. Herein the application of air at a pressure and timesufficient to switch the valve from one state to its other state, i.e.from open to closed or from closed to open, is referred to as “toggling”the valve, and the application of said air in this manner is referred toas a high pressure (pneumatic) control signal. A suitable pneumaticcontrol valve PCV for this application is available in the form of apneumatic latching valve from Norgren Limited of PO Box 22, EasternAvenue, Lichfield, Staffordshire, WS13 6SB, United Kingdom. UK Patentapplication GB 1313622.1 filed on 30 Jul. 2013, the description of whichis appended hereto, and the contents of which are incorporated herein byreference in their entirety, describes such pneumatic latching valves.It will be appreciated that each pneumatic control valve could haveadditional operating states which are cycled through sequentially independence on said pneumatic control signal.

The CTIS 1 further comprises a valve block 3 for controlling the supplyof compressed air to each of the pneumatic control valves PCV. The valveblock 3 is fluidly coupled to a first compressed air source 5 and asecond compressed air source 7. The first compressed air source 5provides air at a high flow rate and low pressure (HF/LP); and thesecond compressed air source 7 is operable to provide air at a higherpressure. As described herein, the first and second compressed airsources 5, 7 are distinct from each other. In the present embodiment,the first compressed air source 5 comprises a first compressor 9; andthe second compressed air source 7 comprises a second compressor 11 anda reservoir 13.

The activation pressure of each said pneumatic control valve PCV isbelow the pressure of the second compressed air source 7. In this mannerthe second compressed air source 7 can be applied for a short durationto switch one or more selected pneumatic control valves PCV from aclosed state to an open state, and vice versa.

An ECU 15 is provided to control operation of the CTIS 1. Specifically,the ECU 15 is configured to control operation of the valve block 3 andthe first compressor 9. The second compressor 11 forms part of thevehicle air suspension and could be controlled indirectly by the ECU 15.

A tire supply line TSL is provided to supply compressed air from thevalve block 3 to each tire T. Specifically, the CTIS 1 comprises a frontleft tire supply line TSL_(FL), a front right tire supply line TSL_(FR),a rear left tire supply line TSL_(RL) and a rear right tire supply lineTSL_(RR). The pneumatic control valves PCV are provided at the ends ofthe tire supply lines TSL to control the supply of compressed air to therespective tires T. A section of each tire supply line TSL extends alongthe respective vehicle axles to supply compressed air to the pneumaticcontrol valves PCV mounted in each wheel hub. A rotary air coupling(RAC) is provided in each tire supply line TSL to provide a fluidcoupling to supply compressed air from the valve block 3 to the sectionof each tire supply line TSL disposed in the vehicle axle.

The valve block 3 will now be described in more detail with reference toFIG. 1B. The valve block 3 comprises first and second inlet valvesV_(INC), V_(INSS). The first inlet valve V_(INC) operatively controlsthe supply of compressed air from the first compressed air source 5which is connected to the valve block 3 by a first supply line 17. Thesecond inlet valve V_(INSS) operatively controls the supply ofcompressed air from the second compressed air source 7 which isconnected to the valve block 3 by a second supply line 19.

The valve block 3 comprises four outlet valves (collectively referencedas V_(O)) for controlling the supply of compressed air to the respectivetire supply lines TSL. In particular, the valve block 3 comprises: afront left outlet valve V_(FLO) for controlling the supply of compressedair to the front left tire supply line TSL_(FL); a rear left outletvalve V_(RLO) for controlling the supply of compressed air to the rearleft tire supply line TSL_(RL); a front right outlet valve V_(FRO) forcontrolling the supply of compressed air to the front right tire supplyline TSL_(FR); and a rear right outlet valve V_(RRO) for controlling thesupply of compressed air to the rear right air supply line TSL_(RR). Theoutlet valves V_(O) are operable independently of each other to enablethe selective supply of compressed air to one or more of the tire supplylines TSL.

The valve block 3 also comprises first and second exhaust valves E₁, E₂coupled to an exhaust line 21. The exhaust line 21 terminates with anexhaust outlet 23 which is open to atmosphere to vent exhaust air fromthe CTIS 1. The first and second exhaust valves E₁, E₂ are operable tocontrol the flow of exhaust air to the exhaust line 21, for exampleduring tire deflation. A safety valve V_(SAFE) is also provided in thevalve block 3. The safety valve V_(SAFE) is operable to vent toatmosphere any excess air which might accumulate in the valve block 3due, for example, to malfunction of any of the components of the CTIS 1.

The inlet valves V_(INC), V_(INSS), the outlet valves V_(O) and theexhaust valves E₁, E₂ are solenoid valves having a normally-closedconfiguration (illustrated by a filled symbol in FIG. 1B). The inletvalves V_(INC), V_(INSS), the outlet valves V_(O) and the exhaust valvesE₁, E₂ are operable independently of each other and are actuated bycontrol signals received from the ECU 15. The safety valve V_(SAFE) isalso a solenoid valve but has a normally-open configuration (illustratedby an open symbol in FIG. 1B). The safety valve V_(SAFE) is closed byreceiving a control signal from the ECU 15.

The first compressor 9 is a dedicated compressor for the CTIS 1. Thesecond compressor 11 forms part of an air suspension system (not shown).The first and second compressors 9, 11 are controlled, directly orindirectly, by the ECU 15. The first compressor 9 comprises an electricmotor 27 and has an operating pressure of approximately 9 bar. A dryerunit 29 is coupled to the compressor 9 partway through a firstcompressed air supply line 31 connecting the first compressor 9 to thevalve block 3. The air suspension system comprises pneumatic actuators(not shown) which connect the chassis (not shown) of the vehicle VH tothe wheels W. The pneumatic actuators are operable to maintain thevehicle at a target ride height and optionally also to request rideheight changes (for example to improve off-road performance or ease ofaccess/loading). Compressed air at a pressure of up to 20 bar is storedin the reservoir 13.

A fluid gallery 33 is provided in the valve block 3. The gallery 33 isopen to each of: the outlet valves V_(O), the inlet valves V_(INC),V_(INSS), the exhaust valves E₁, E₂, and the safety valve V_(SAFE). Thevalve block 3 houses a pressure sensor 35 arranged to measure thepressure in a gallery 33. The gallery 33 can be selectively placed influid communication with one or more of the tire supply lines TSL byopening one or more of the outlet valves V_(O). In the presentembodiment, the pressure sensor 35 measures the pressure in theindividual tire supply lines TSL by placing the tire supply line TSL influid communication with the gallery 33. By opening the pneumaticcontrol valve PCV associated with that tire supply line TSL, thepressure sensor 35 can measure the air pressure in the tire cavity(hereinafter referred to, for simplicity, as the tire pressure).

The gallery 33 receives compressed air from each of said first andsecond compressed air sources 9, 11 via the respective first and secondinlet valves V_(INC), V_(INSS). The first inlet valve V_(INC) isoperable to control the supply of compressed air from the firstcompressed air source 5 to the gallery 33. The second inlet valveV_(INSS) is operable to control the supply of compressed air from thesecond compressed air source 7 to the gallery 33. In use, the firstcompressed air source 5 is the primary source of compressed air forinflating the tires T. One or more of the tire supply lines TSL can beplaced in communication with the first compressed air source 5 byopening the first inlet valve V_(INC) and the appropriate outlet valvesV_(O). The second compressed air source 7 provides a higher pressuresupply which is controlled by the second inlet valve V_(INSS) togenerate a pneumatic control signal as described above for controllingoperation of one or more of said pneumatic control valves PCV to tiresfor which the respective outlet valves V_(O) are open, i.e. to togglethe valves from one stable state to the other stable state.Specifically, the second inlet valve V_(INSS) is operated to generatethe pneumatic control signal to cycle the pneumatic control valve(s) PCVin communication with the gallery 33. The pneumatic control valve(s) PCVcycle through their respective operating states in response to thepneumatic control signal and, therefore, can be operated to control thesupply of compressed air to and from the respective tires T. By openingthe pneumatic control valve(s) PCV, one or more of the tires T can beplaced in communication with the respective tire supply lines TSL. Thevalve block 3 can be operated to place the tire supply lines TSL incommunication with the first compressed air source 5 to inflate one ormore of said tires T; or in communication with the exhaust line 21 todeflate one or more of said tires T. Furthermore, the valve block 3 canbe operated to measure the pressure of the air in the tires T.

To measure an individual tire pressure of a wheel having a closed PCV,the valve block 3 is operated to close the first and second inlet valvesV_(INC), V_(INSS), and the exhaust valves E₁, E₂. The outlet valve V_(O)corresponding to the tire supply line TSL for the particular tire isopened to place the tire supply line TSL in fluid communication with thegallery 33. A pneumatic control signal is then generated by operatingthe second inlet valve V_(INSS) to open the pneumatic control valve PCVfor that tire T. The tire T is thereby placed in communication with thegallery 33 via the corresponding tire supply line TSL. The pressuresensor 35 then measures the air pressure in the gallery 33 to determinethe tire pressure for that particular tire T. Once the pressure has beenmeasured, if no further action is required in relation to that tire apneumatic control signal may be generated by operating the second inletvalve V_(INSS) to close the pneumatic control valve PCV.

The CTIS 1 according to the present embodiment uses a single pressuresensor 35 for measuring the pressure in the gallery 33. It will beappreciated that more than one pressure sensor 35 could be provided. Forexample, a pressure sensor 35 could be provided in communication witheach tire supply line TSL. Equally, a separate valve block 3 could beprovided for each tire T or for each axle.

The ECU 15 is programmed to control the overall operation of the CTIS 1.The ECU 15 is configured to determine an inflation time or a deflationtime. The inflation time is the period of time over which compressed airmust be supplied from the first compressed air source 5 to the one ormore tire(s) T to reach the target tire pressure. The inflation time isa function of one or more of the following: the pressure differentialbetween the target tire pressure and the current tire pressure (thecurrent tire pressure being the tire pressure prior to inflation); theoperating characteristics of the first compressed air source (e.g.nominal pressure and flow rate); the number of tires T which are beinginflated at any given time (if more than one tire T can be inflatedsimultaneously); and the volume and/or temperature of the tire cavities.It will be appreciated that is not necessarily equivalent to acompressor run time as the compressed air generated by the firstcompressor 9 is buffered in the first reservoir.

The deflation time is the period of time over which compressed air mustbe vented from the one or more tire(s) T through the first and secondexhaust valves E₁, E₂ to reach the target tire pressure. The deflationtime is also a function of the number of tires T being simultaneouslydeflated, of the current tire pressure (i.e. the tire pressure beforedeflation), of the target tire pressure and/or the pressure differentialto be achieved by tire deflation and/or of the volume and/or temperatureof the tire cavities.

In the present embodiment, the ECU 15 retrieves the inflation timeand/or the deflation time from a look-up table stored in a memory deviceaccessible to the ECU 15. The look-up table can take the form of adouble entry table indexed according to the current tire pressure andthe target tire pressure. Based on the current tire pressure and thetarget tire pressure, the ECU 15 can retrieve from the look-up table avalue corresponding to, or representative of, the predetermined tireinflation time for a given flow rate and air supply air pressure.Alternatively the look-up table may give a volume of air required andthe ECU calculates the inflation time based on measured or estimatedpressures and flow rates and the retrieved volumetric air requirement.Other methods may be useful.

The ECU 15 controls tire inflation and/or deflation by opening andclosing, as appropriate, the various valves V_(O), V_(INC), V_(INSS),E₁, E₂ of the valve block 3. Tire inflation and deflation can thuspotentially be performed one tire T at a time, or according to anycombination of tires T simultaneously. In the present embodiment,however, the ECU 15 is programmed to simultaneously deflate all thetires T, or in pairs, and to inflate the tires T one at a time or,simultaneously in pairs. If deflated/inflated in pairs, the pairs oftires T are selected according to their location at the front or rear ofthe vehicle VH. In this event, the tires T are said to bedeflated/inflated by the CTIS 1 ‘per axle’.

In the present embodiment, the ECU 15 uses an algorithm to refer thecurrent and target tire pressures to a nominal tire temperature of 25°C. and to the case of tire inflation of an individual tire T.Alternatively, different look-up tables each corresponding to a tiretemperature and/or to the case of tire inflation for two or more tires Tcould be used. Compressed air losses in the CTIS 1 may affect the periodof time taken for the CTIS 1 to achieve a predetermined pressure. Thevalues stored in the look-up table could be dynamically updated to takeinto account the effects of said losses. The values could, for example,be updated via one or more self-learning algorithms.

The ECU 15 is in addition configured to provide information relating tothe status and/or operation of the CTIS 1 to a vehicle user via ahuman-machine interface (HMI) 37. A dashboard (not shown) of the vehicleVH is in addition equipped with a visual output, for example a tireoperation dial 39, to provide a user with information as to whethercompressed air is being supplied to, or exhausted from, the tirecavities.

FIG. 1C illustrates the relationship between the main mechanicalcomponents of the CTIS 1 described herein (which incorporates the valveblock 3 illustrated in FIG. 1B) and a vehicle control system 41. Thevehicle control system 41 comprises the ECU 15. The ECU 15 is programmedto implement the control strategies and procedures described herein. Inthis embodiment, the ECU 15 receives from a tire pressure monitoringsystem (TPMS) 43, via a vehicle controller area network (CAN) 45,real-time information relating to the current tire pressures for thefour tires T of the vehicle VH. The pressure sensor communicatesdirectly with the ECU 15 via electric signals representative of thepressure measured by the pressure sensor 35 in the gallery 33 of thevalve block 3. As described earlier, the pneumatic control valves PCVand the various valves V, I, E of the valve block 3 can be configuredsuch that the pressure sensor 35 measures a pressure which isrepresentative of the pressure inside each of the tires T. The TPMS 43also monitors the temperature inside the tires T so that the tirepressures can be referred to a nominal temperature of 25 degrees C.using appropriate algorithms, for example a thermocouple or otherthermal sensor may be located in or through the hub of each wheel.

The ECU 15 implements tire inflation and/or deflation strategies asdescribed herein on the basis of the relationship between the targettire pressures and the current tire pressures as measured by the TPMS 43and/or pressure sensor 35. To do this, the ECU 15 is required to controlthe various mechanical components of the CTIS 1. As seen in FIG. 1C, theECU 15 is configured to control the outlet valves V_(O) via a pulsewidth modulation (PWM) control network 47. Via the same PWM controlnetwork 47, the ECU 15 also controls the purging function of the dryerunit 29, the electric motor 27 which drives the compressor 9, the firstand second inlet valves V_(INC), V_(INSS), the exhaust valves E₁, E₂ andthe safety valve V_(SAFE). As described herein, the target tirepressures can be manually selected by the driver of the vehicle via thehuman-to-machine interface (HMI) 37 or they can be automaticallyselected by the vehicle control system 41 on the basis of otherinformation including vehicle driving modes. The HMI 37 communicateswith the ECU 15 via the vehicle CAN 45. As an alternative to PWM controlfull cycle on/off solenoid valves could be used.

A first block diagram 100 illustrating the operating modes of the CTIS 1is show in FIG. 2. The CTIS 1 is initially switched off (STEP 101). Inthe present embodiment, the CTIS 1 can be switched off by a vehicle usercommand and/or by switching off the engine of the vehicle VH (CONDITION103). When the engine is started (CONDITION 105) the CTIS 1 carries outan initial system check (STEP 107). If the initial system check detectsa preliminary fault (CONDITION 109), e.g. compressor malfunction, theCTIS 1 enters a System Fault Mode (STEP 111) and the vehicle user isinformed accordingly. If the initial check is successful (CONDITION 113)the CTIS 1 is ready to be switched on. When the CTIS 1 is then switchedon by a user command (CONDITION 115), the CTIS 1 performs a systemstart-up check (STEP 117) to check that the components of the CTIS 1 arecorrectly working together and therefore capable of deliveringcompressed air to the tires T. If a fault is detected (CONDITION 119)the CTIS 1 enters the System Fault Mode (STEP 111) and the vehicle useris informed accordingly. If the check is successful (CONDITION 121) theCTIS 1 enters a Maintain Pressure Mode (STEP 123).

In the Maintain Pressure Mode (STEP 123), the CTIS 1 operates to ensurethat a target tire pressure substantially equals a current tire pressure(CONDITION 125) for each of the tires T or for any selected tirecombination (e.g. for the rear axle tires). If for any of the tires Tthe target tire pressure is greater than the current tire pressure(CONDITION 127), the CTIS 1 switches to an Inflate Mode (STEP 129). Onthe basis of the pressure difference between the target and current tirepressures, the ECU 15 retrieves an inflation time from a look-up tablestored in a memory in the ECU 15.

When the inflation time has elapsed (CONDITION 131) for each tire T orfor each combination of tires being simultaneously inflated, the CTIS 1returns to the Maintain Pressure Mode (STEP 123).

If the current tire pressure is greater than the target tire pressure(CONDITION 133), the CTIS 1 enters a Deflate Mode (STEP 135). In thedeflate mode, compressed air is vented from one or more tires Tsimultaneously and routed via one or more of the tire supply lines TSLto the valve block 3 and, from there, to atmosphere through the exhaustvalves E₁, E₂, the exhaust outlet 23 and exhaust port 25. On the basisof the pressure difference between the target and current tirepressures, the ECU 15 retrieves the deflation time from the look-uptable stored in a memory in the ECU 15. When the current/actual tirepressure reaches or substantially matches the target tire pressure(CONDITION 137) the CTIS 1 returns to the Maintain Pressure Mode (STEP123).

If a fault develops during the Inflate Mode (STEP 129), or during theDeflate Mode (STEP 135), the CTIS 1 enters the System Fault Mode (STEP111).

The target tire pressures can vary between different tires T and for allthe tires T dependent on the vehicle driving mode. This will now bedescribed with reference to a second block diagram 200 shown FIG. 3. Thesecond block diagram 200 illustrates the four main vehicle drivingmodes, namely: an Economy Mode (Step 201); an On Road Mode (STEP 203);an Off Road Mode (STEP 205) and a Recovery Mode (STEP 207) (listed indecreasing order of target tire pressures). The Economy Mode (STEP 201)requires a target tire pressure of 2.8 bar for the front tires T_(FL),T_(FR) and 3.0 bar for the rear tires T_(RR), T_(RL). The On Road Mode(STEP 203) requires a target tire pressure of 2.3 bar for the fronttires T_(FL), T_(FR) and 2.5 bar for the rear tires T_(RR), T_(RL). TheOff Road Mode (STEP 205) requires a target tire pressure of 1.5 bar bothfor the front and rear tires T_(FL), T_(FR), T_(RR), T_(RL). TheRecovery Mode (STEP 207) requires a target tire pressure of 1.2 bar bothfor the front and rear tires T_(FL), T_(FR), T_(RR), T_(RL). It will beapparent to the skilled person that these tire pressures are exemplaryonly and that actual tire pressures for different conditions will bedependent upon the specific tires and/or other factors.

When the vehicle switches from the Off Road Mode (STEP 205) to the OnRoad Mode (STEP 203), it is appropriate to inflate the tires to achievethe target tire pressure for the On Road Mode. The transition from theOff Road Mode (STEP 205) to the On Road Mode (203) can, for example, beperformed automatically when the ECU 15 determines that the vehiclespeed is greater than a reference threshold speed; or in dependence on adriver request. The ECU 15 enters an interim tire inflation mode (STEP209). The ECU 15 is configured to inflate the tires T in two, distinctstages. The tire inflation procedure is performed ‘per axle’. In a firstphase (STEP 211), the ECU 15 inflates both the front and rear tiresT_(FL), T_(FR), T_(RR), T_(RL) from the current tire pressures to anintermediate target tire pressure of, for example 2.0 bar. In a secondphase (STEP 213), the ECU 15 inflates both the front and rear tiresT_(FL), T_(FR), T_(RR), T_(RL) from the intermediate target tirepressure to the target tire pressures of 2.3 bar for the front tiresT_(FL), T_(FR) and 2.5 bar for the rear tires T_(RR), T_(RL), asspecified in the On Road Mode (STEP 203). In the described embodiment,the intermediate target tire pressure has been set to 2.0 bar to satisfya local legal requirement. However, other selection criteria forselecting the intermediate target tire pressure could be used, in anycase the intermediate pressure will be a pressure at which it isappropriate for the vehicle to be driven on a road. It will beappreciated that the tires T could be inflated in more than two stages.

In the present embodiment, the first phase (STEP 211) performed by theCTIS 1 requires less than one minute to inflate the tires T from theircurrent tire pressure in the Off Road Mode (STEP 205) to theintermediate target tire pressure of 2.0 bar and the second phase (STEP213) takes longer than one minute to successively inflate the tires Tfrom the intermediate target tire pressure of 2.0 bar to the target tirepressures specified in the On Road Mode 51. The first phase (STEP 211)can be performed when the vehicle/vehicle VH is still off road, or whenthe vehicle VH is about to enter the road, followed by the second phase(STEP 213) which is performed subsequently, for example when the vehicleis on the road.

A first recovery Mode (STEP 207) is activated to recover the vehicle VH,for example when a vehicle belly-out event occurs. A vehicle belly-outevent refers to a situation in which the vehicle body is partially orcompletely supported by the ground under the vehicle instead of beingsupported by the tires T. The Recovery Mode (STEP 207) can be activatedautomatically by the ECU 15; or by the driver of the vehicle. When theRecovery Mode (STEP 207) is activated, the vehicle verifies whether anadjustable ride height of the vehicle is in the highest position settingand if not the ECU controls the suspension to raise the vehicle and theCTIS 1 operates to reduce the pressure of the front tires T_(FL), T_(FR)and the rear tires T_(RR), T_(RL). to, for example, 1.2 bar. TheRecovery Mode (STEP 207) is only activated when the vehicle VH is in theOff Road Mode 205. By decreasing the tire pressure a larger surface areaof the tire will come into contact with the ground that will increasetraction between the wheel and the surface, thereby assisting inreducing wheel slip and moving the vehicle, and increasing the rideheight will lift the vehicle body slightly to raise it of the ground.

A second recovery mode is activated to recover the vehicle VH, forexample when a vehicle becomes bogged down in sand or mud, i.e. thetires are spinning and have dug into the surface, but prior to thevehicle bellying out. The second recovery mode can be activatedautomatically by the ECU 15; or by the driver of the vehicle. When thesecond recovery mode is activated, the CTIS 1 operates to reduce thepressure of the front tires T_(FL), T_(FR) and the rear tires T_(RR),T_(RL). to, for example, 1.2 bar. The second recovery mode is onlyactivated when the vehicle VH is in the Off Road Mode 205. By decreasingthe tire pressure a larger surface area of the tire will come intocontact with the ground that will increase traction between the wheeland the surface, thereby assisting in reducing wheel slip and moving thevehicle.

The Economy Mode (STEP 201) can be selectively activated by the user, orautomatically by the ECU 15, for example based on vehicle speed. Whenthe Economy Mode (STEP 201) is activated, the CTIS 1 operates toincrease the pressure of the front tires T_(FL), T_(FR) to, for example,2.8 bar; and to the rear tires T_(RR), T_(RL) to, for example, 3.0 bar.The increase in tire pressure can be performed in a single phase ormultiple phases, for example to maintain the pressure differentialbetween the front and rear tire pressures within a predefined margin.The Economy Mode (STEP 201) can be activated only when the vehicle is inthe On Road Mode (STEP 203).

In the described embodiment, the Off Road Mode (STEP 205) needs to bemanually requested by the driver. When the driver requests the Off RoadMode (STEP 205), the ECU 15 is programmed to deflate the tires T to thetarget tire pressure defined in the Off Road Mode (STEP 205). In thedescribed embodiment, the tire deflation from the On Road Mode (STEP203) to the Off Road Mode (STEP 205) lasts approximately 2.5 minutes(i.e. it is comparatively slower than the tire inflation procedure). Thetire deflation from the On Road Mode to the Off Road mode can beperformed on all four tires T at the same time.

The target tire pressures are set depending on the vehicle driving mode,as illustrated in FIG. 3. The actual or current tire pressure can bemeasured by the pressure sensor 35 coupled to the gallery 33 disposed inthe valve block 3. Alternatively and/or additionally, the actual orcurrent tire pressure is measured by a tire pressure monitoring system(TPMS) 43 provided on the vehicle VH (as shown in FIG. 1C). The TPMS 43is responsible for providing the vehicle control system 9 withcontinuous information on the current tire pressures. The pressuresensor 35 is used to check the tire pressures after tire inflationand/or deflation. The TPMS 43 communicates wirelessly with a sensorprovided in each tire T.

Depending on the relationship between the target and current tirepressures, the ECU 15 may be configured to implement inflation anddeflation strategies to try to maintain the current tire pressure asclose as possible to, or equal to, the target tire pressures. A thirdblock diagram 300 in FIG. 4 illustrates in more detail the strategy formaintaining the target tire pressures. Alternatively, or in addition,the present control strategy may be used for increasing and decreasingpressure in response to driver commands for different operating modeswithout the need to continuously attempt to maintain the pressure.

The TPMS 43 operates to measure the pressure of each tire T (STEP 301).A comparison is made between the measured (actual) tire pressure and atarget tire pressure (STEP 303). If the target tire pressures for one ormore of the tires T exceed the current tire pressure and the differencebetween the target tire pressures and the current tire pressures isgreater than a predetermined reference pressure difference threshold(CONDITION 305), the ECU 15 is programmed to implement an Inflate PerAxle strategy (STEP 307). On the basis of the pressure differencebetween the target and current tire pressures, the ECU 15 firstretrieves from memory the inflation time required to inflate each of thetires T_(FL), T_(FR), T_(RR), T_(RL) as shown in FIG. 4. Then, the ECU15 controls the valve block 3 to inflate the tires of the rear axleT_(RR), T_(RL). Once the rear tires T_(RR), T_(RL) have been inflated,the ECU 15 controls the valve block 3 to inflate the tires of the frontaxle T_(FL), T_(FR). If there is a pressure difference discrepancybetween right T_(FR), T_(RR) and left tires T_(FL), T_(RL) thecorresponding right V_(FR), V_(RR) and left V_(FL), V_(RL) outlet valvescan be opened for different time periods to compensate for such adiscrepancy.

By using this staggered tire inflation strategy, the dynamic stabilityor handling balance of the vehicle 2 can be preserved during the tireinflation procedure. By inflating the tires of the rear axle T_(RR),T_(RL) followed by the tires of the front axle T_(FL), T_(FR), thehandling characteristics of the vehicle VH can be biased towardsundersteer (rather than oversteer). In a driving experience ideally theuser does not experience a change in driving dynamics, i.e. the mannerin which the vehicle responds to the same input commands (e.g. steeringwheel angle and throttle position). However driving dynamic is relatedto tire pressures and changing these dynamically while the vehicle ismoving may affect driving dynamics. In order to minimize any perceivedchange to the driver the change is biased towards understeer during thechange as an experience of understeer is less likely to cause the driverto experience a feeling of loss of composure of the vehicle than a biastowards overseer.

If the current tire pressure exceeds the target tire pressure and thedifference between the current tire pressure and the target tirepressure is less than a predetermined reference pressure differencethreshold (CONDITION 309), the CTIS 1 enters into a Deflate All Tires atOnce mode (STEP 311). A deflate all tires at once strategy is describedbelow with reference to FIG. 5.

If the current tire pressure exceeds the target tire pressure and thedifference between the current tire pressure and the target tirepressure is greater than a predetermined reference pressure differencethreshold and the vehicle operating mode is set on On Road Mode 51(CONDITION 313), the ECU 15 is programmed to enter the CTIS 1 into aDeflate Per Axle strategy (STEP 315). A reverse staggered deflationlogic is then applied by the CTIS 1 compared to the staggered InflationPer Axle (STEP 307) described above. The front axle tires T_(FL), T_(FR)are first deflated to the required target pressure and the rear axletires T_(RR), T_(RL) are deflated subsequently until the required targetpressure is reached. This is done in order to maintain dynamic vehiclestability as explained above to bias any change in vehicle handlingtowards understeer rather than oversteer.

A fourth block diagram 400 shown in FIG. 5 illustrates in more detailthe Deflate All Tires at Once strategy (STEP 311) illustrated in FIG. 4.When the CTIS 1 enters the Deflate All Tires at Once strategy (STEP311), the ECU 15 outputs a first signal S₁ to start a Deflate strategy(MODE 401). The outlet valves V_(O) are opened (STEP 403) and the secondinlet valve V_(INSS) is toggled (i.e. opened and closed) so that thesecond compressed air source 7 generates a pneumatic control signal toopen the pneumatic control valves PCV. The exhaust valves E₁, E₂ arethen opened (STEP 407) and tire deflation commences. After apredetermined time period (retrieved by the ECU 15 from the look-uptable stored in memory), the outlet valves V_(O) are closed (STEP 409).The outlet valves V_(O) may be closed on an individually timed basis toachieve the desired opening time of each outlet valve V_(O). The ECU 15produces a signal which causes the CTIS 1 to enter a Measure procedure(STEP 411).

In the Measure procedure (MODE 411), the exhaust valves E₁, E₂ areclosed (STEP 415) and the outlet valves V_(O) are opened individually,i.e. one at a time (STEP 413). The first one of the outlet valves V_(O)may be opened substantially at the same time as the exhaust valves areclosed, or alternatively the exhaust valves may be closed prior toopening any of the outlet valves. The pressure sensor 35 measures thepressure in the gallery 33, which is representative of the tire pressureof the tire T being measured (STEP 417). If, for any of the tires T, themeasured tire pressure is greater than the target pressure (CONDITION419), the exhaust valves E₁, E₂ are opened (STEP 421). Since thepneumatic control valve PCV corresponding to the tire being measured isstill in the open position, compressed air is vented from the CTIS 1 andthe relevant tire T is deflated further until measured tire pressurematches the target pressure. The procedure is repeated for the otherthree tires T, until the tire pressure of each of the four tires Tmatches the respective target pressure. Optionally tires on one axel maybe measured/further deflated before moving on to the other axle. Beforea tire pressure measurement for another tire T is taken, however, theoutlet valve V_(O) relating to the tire being measured is closed. Thetarget tire pressure for the front tires T_(FL), T_(FR) and the reartires T_(RR), T_(RL) tires can be the same (as in the case of the OffRoad Mode 205) or can be different (as in the case of the Economy Mode203). When the target tire pressure has been reached for all of thetires T, a strategy is implemented to close the pneumatic control valvesPCV (MODE 423) is initiated by the ECU 15.

To close the pneumatic control valves PCV, a pneumatic control signal isgenerated by the second compressed air source 7 to cause the pneumaticcontrol valves PCV to close for each tire T. This is achieved bytoggling the LF/HP inlet valve V_(INSS) (STEP 425). The exhaust valvesE₁, E₂ are then also toggled, i.e. opened and then subsequently closed,to vent the air still present in the relevant tire supply line TSL torestore atmospheric pressure in this tire supply line TSL (STEP 427).The pressure sensor 35 can then measure a pressure in the gallery 33representative of the pressure in this tire supply line TSL to checkthat the pneumatic control valve PCV associated with each tire has beensuccessfully closed (STEP 429). If the latching is successful, thepressure sensor 35 measures a pressure equal to, or approximately equalto, atmospheric pressure. If latching is not successful (CONDITION 431),the latching procedure is repeated. If the latching has been successful,the relevant outlet valve V_(O) is closed to isolate the respective tiresupply line TSL. The procedure is later repeated for each of theremaining outlet valves V_(O) of the valve block 3 (STEP 433), after thetire pressure of each of the tires T has been measured according to theMeasure procedure (MODE 411).

It will be appreciated that the second inlet valve V_(INSS) can becontrolled to generate a pneumatic control signal for actuating a singlepneumatic control valve PCV or for actuating a plurality of saidpneumatic control valves PCV simultaneously. The outlet valve(s) V_(O)can be opened or closed to communicate the pneumatic control signalalong the appropriate tire supply lines TSL to control said one or morepneumatic control valves PCV. By controlling several pneumatic controlvalves PCV at the same time (for example to open or close them inunison), a time saving may be achieved.

When all the tires have reached the target tire pressure and all thepneumatic control valves PCV have been latched, the exhaust valves E₁,E₂ are opened (STEP 435).

A fifth block diagram 500 is shown in FIG. 6 to illustrate the InflatePer Axle strategy (STEP 307) illustrated in FIG. 4. The ECU 15 generatesa second signal S₂ to initiate the Inflate mode (STEP 501) to inflatethe tires T on each axle in sequence. As outlined herein, the tires T onthe rear axle are inflated first, and then the tires T on the front axleare inflated. The first inlet valve V_(INC) is opened and the compressor9 is activated (STEP 505). The airflow from the compressor 9 isestimated based on the current/voltage drawn by the compressor 9 (whichindicates the work done compressing the air) optionally together withpressure/temperature information (which approximates the density of airdrawn into the compressor 9). A performance table for the compressor 9is typically available from the supplier to enable the airflow to beestimated. As the tire pressure rises, the compressor 9 will be workingagainst a higher pressure so the flow rate of air delivered to the tiresupply line will change dynamically.

The ECU 15 accesses the stored look-up table to determine the inflationtime for each outlet valve (the front outlet valves V_(FL), V_(FR) orrear outlet valves V_(RL), V_(RR)). The relevant outlet valves V_(O)(the front outlet valves V_(FL), V_(FR); or the rear outlet valvesV_(RL), V_(RR)) are then opened (STEP 507). The second inlet valveV_(INSS) is controlled to toggle the pneumatic control valves PCV forthe tires T to an open position (if they are not already in an openstate). It will be appreciated that the second inlet valve V_(INSS) canbe controlled to generate a pneumatic control signal for controllingmore than one pneumatic control valve PCV simultaneously when thecorresponding outlet valves V_(O) are open. The outlet valves V_(O) areclosed when the compressed air has been delivered to achieve the targetpressure (STEP 509). At this stage, the first inlet valve V_(INC) isalso closed, and the dryer unit 29 may optionally be purged from waterremoved from the delivered compressed air (STEP 511).

When all the tires T have been inflated, i.e. when the Inflate mode(STEP 501) has been repeated for the other axle (CONDITION 513), theexhaust valves E₁, E₂ are opened to purge excess compressed air from thevalve block 3 (STEP 513) so that the Measure mode (STEP 515) can beperformed. The pneumatic control valves PCV for all of the tires T arethen closed (STEP 517). These procedures are unchanged from thosedescribed herein with reference to FIG. 5 for each of the tires T inanticlockwise sequence. When the target tire pressure for all the tiresT has been reached and all the pneumatic control valves PCV have beenclosed (CONDITION 519), the exhaust valves E₁, E₂ are closed (STEP 521).If the target tire pressure has not been reached or any of the pneumaticcontrol valves PCV remain open, the appropriate procedures (STEP 515 andSTEP 517) are repeated.

A sixth block diagram 600 is shown in FIG. 7 to illustrate in moredetail the Deflate Per Axle strategy (STEP 315). When the entryconditions are satisfied, the ECU 15 causes the CTIS 1 to enter theDeflate Per Axle strategy (STEP 315). The ECU 15 produces a third signalS₃ to cause the CTIS 1 to start the Deflate procedure (STEP 601). Allthe outlet valves V_(O) associated with one of the axles (the frontoutlet valves V_(FL), V_(FR) or rear outlet valves V_(RL), V_(RR)) areinitially opened (STEP 603). The second inlet valve V_(INSS) is toggled(STEP 605) to open the pneumatic control valves PCV in the relevantaxle. The exhaust valves E₁, E₂ are then opened (STEP 607) so that thedeflation of the tires T connected to the relevant axle commences. Acheck (STEP 609) is then performed to ensure that only the appropriateoutlet valves V_(O) associated with each axle are open (the front outletvalves V_(FL), V_(FR) or the rear outlet valves V_(RL), V_(RR)).

When the outlet valves (the front outlet valves V_(FL), V_(FR) or rearoutlet valves V_(RL), V_(RR)) have been opened for the desired timeperiod to reach the target amount of compressed air removed from thetires T, the outlet valves V_(O) are closed (STEP 611). The procedure isrepeated if the tires connected to the other axle need also to bedeflated (CONDITION 613).

When all the tires T have been deflated, the Measure procedure (STEP615) and the procedure to close the pneumatic control valves PCV (STEP617) are carried out. These procedures are the same as those describedherein with reference to FIG. 5. When the target tire pressure for allthe tires T has been reached and all the pneumatic control valves PCVhave been closed (CONDITION 619), the exhaust valves E₁, E₂ are closed(STEP 621). It will be appreciated that the deflation procedure can beperformed with a single toggle (open/closed) of the appropriatepneumatic control valve(s) PCV. The deflation of the tire(s) T isthereafter controlled by the outlet valves V_(O) in the valve block 3.It is not necessary to toggle the pneumatic control valve(s) PCV betweenaxle deflations. Rather, the pneumatic control valve(s) PCV remain openfollowing deflation for measurement (STEP 614) before being closedtogether.

As illustrated by FIG. 7, the CTIS 1 can also deflate all four tires Tof the vehicle VH by first deflating two tires T of one of the axles (inthe described embodiment, the tires mounted to the front axle T_(FL),T_(FR) are deflated first, as described above), and then the other twotires T of the other one of the axles. This tire deflation strategy isalso referred to as per axle deflation. Alternatively, the CTIS 1 candeflate the four tires T one tire T at a time, i.e. the tires T can beindividually deflated, measured and closed via the procedure for closingthe pneumatic control valves PCV.

As illustrated by FIG. 6, the CTIS 1 can inflate all four tires T of thevehicle VH by first inflating the two tires T of one of the axles (inthe present embodiment, the tires mounted to the rear axle T_(RL),T_(RR) are inflated first), and then the other two tires T of the otherone of the axles. Alternatively, the CTIS 1 can inflate all four tires Tindividually. The CTIS 1 is not designed to inflate all four tires Tsimultaneously due to the flow rate and maximum pressure limitations ofthe compressor 9. However, it will be understood that it is in principlepossible to adapt the CTIS 1 to simultaneously inflate all the tires T,by using a compressor 9 with an adequate flow-rate and pressure rating.

The valve usage per unit time will now be considered. A completeinflation or deflation event (i.e. including tire inflation or tiredeflation, tire pressure measurement and latching of the pneumaticcontrol valve PCV), which may involve some or all of the tires T, isreferred to herein as a complete tire inflation or deflation cycle. Thisis in contrast to tire inflation or deflation (operations) which, asdescribed above, only relates to the presence of compressed air flow(into or out from the tires T). It will be appreciated that, inpractice, the CTIS 1 may be required to change the tire pressure of onlysome of the tires T. A first table 710 shown in FIG. 8 summarizes valveusage for a complete tire deflation cycle involving simultaneousdeflation of all four of the tires T.

The first table 710 refers to deflation of all the tires to 1.5 bar, asdescribed in FIG. 3 in connection with the passage of the vehicle fromthe On Road mode 203 to the Off Road mode 205. A first column 711 of thefirst table 710 lists the inlet valves V_(INC), V_(INSS), the outletvalves V_(O) and the exhaust valves V of the CTIS valve block 3. Asecond column 712 counts, for each of the valves listed in the firstcolumn 711, the respective valve cycles in the Deflate procedure 401illustrated in FIG. 5. For each of the tires T, a third 713, fourth 714,fifth 715 and sixth 716 column of the first table 710 list therespective valve cycles during the Measure procedure 411 and ClosePneumatic control valve procedure 423 of FIG. 5. A seventh column 717lists the total of the valve cycles for each of the valves listed in thefirst column 711. If after a measurement there is a need to deflatefurther a tire, the exhaust valves E₁, E₂ undergo the same number ofcycles as described in the last two rows 718 of the first table 710 plusone cycle for each of the exhaust valves.

A second table 720 shown in FIG. 9 summarizes similar valve usageinformation for a deflation procedure wherein the tires T are deflatedindividually (this procedure is not illustrated in FIGS. 4 to 7, and isused in connection with the passage of the vehicle from the Economy Mode201 to the On Road Mode 203 of FIG. 3). In this procedure, all of theoutlet valves V_(O) of the valve block 3 are first opened together asillustrated by step 403 of FIG. 5. This allows the CTIS 1 to be preparedfor deflation. Then, each of the tires T_(FL), T_(FR), T_(RR), T_(RL) isindividually deflated until the target tire pressures of the On RoadMode 203 illustrated in FIG. 3 are reached. For this reason, the valvecycle count for each of the corresponding outlet valves V_(FL), V_(FR),V_(RR), V_(RL) in a second column 721 of the second table 720 isdifferent compared to the second column 712 of the first table 710, withthe outlet valves V_(FL), V_(FR), V_(RR), V_(RL) now counting two valvecycles each instead of one. Likewise, if after a measurement there is aneed to deflate further each tire T_(FL), T_(FR), T_(RR), T_(RL), thedeflation procedure is individually repeated, and the exhaust valves E₁,E₂ undergo the same number of cycles as described in the last two rows721 of the second table 720 plus one cycle for each of the exhaustvalves E₁, E₂.

A third table 730 shown in FIG. 10 summarizes similar valve usageinformation for a tire inflation cycle where the tires T are inflatedfrom the target pressures of the Off Road Mode 205 to the targetpressures of the On Road Mode 203 of FIG. 3 via the Interim tireinflation step 209, also shown in FIG. 3. The third table 730 is dividedin five main table sections 731, 732, 733, 734, 735. The first tablesection 731 relates to the inflation of the tires of the rear axleT_(RR), T_(RL) from 1.5 bar to 2.0 bar according to Inflate procedure501, Measure procedure 515 and Close Pneumatic control valve procedure517 of FIG. 6. The columns in this first table section 731 list thevalve cycle counts for each valve V_(O), V_(INC), V_(INSS), E₁, E₂ ofthe valve block 3 and for each procedure. The second table section 732relates to the inflation of the tires of the front axle T_(FL), T_(FR)from 1.5 bar to 2.0 bar also according to Inflate procedure 501, Measureprocedure 515 and Close Pneumatic control valve procedure 517 of FIG. 6.Likewise, the columns in the second table section 732 list the valvecycle counts for each valve V_(O), V_(INC), V_(INSS), E₁, E₂ of thevalve block 3 and for each procedure. The third table section 733relates to the inflation of the tires of the rear axle T_(RR), T_(RL)from 2.0 bar to 2.5 bar. However, in this sequence the rear tiresT_(RR), T_(RL) are inflated, measured and then the correspondingpneumatic control valves PCV_(RR), PCV_(RL) closed individually insteadof being closed per axle as was the case for the previous two tablesections 731, 732. The columns in the third table section 733 list thevalve cycle counts for each valve V_(O), V_(INC), V_(INSS), E₁, E₂ ofthe valve block 3 and for each individual procedure. The fourth tablesection 144 of the third table 140 relates to the inflation of the tiresof the front axle T_(FL), T_(FR) from 2.0 bar to 2.3 bar. Likewise, inthis sequence the front tires T_(FL), T_(FR) are inflated, measured andthe corresponding pneumatic control valves PCV_(FL), PCV_(FR) closedindividually. The columns in the fourth table section 734 of the thirdtable 730 list the valve cycle counts for each valve V_(O), V_(INC),V_(INSS), E₁, E₂ of the valve block 3 and for each individual procedure.The fifth table section 735 summarizes the total valve cycles for thesevalves V_(O), V_(INC), V_(INSS), E₁, E₂.

A fourth table 740 is shown in FIG. 11 and summarizes similar valveusage information for a tire inflation cycle wherein the tires T areinflated from the target pressures of the On Road Mode 203 to the targetpressures of the Economy Mode 201. The fourth table 740 is divided inthree table sections 741, 742, 743. The first table section 741 of thefourth table 740 is equivalent to the third table section 733 of thethird table 730, and the second table section 742 of the fourth table740 is equivalent to the fourth table section 734 of the third table730. The third table section 743 of the fourth table 740 represents thetotal valve cycles in the inflation procedure for the same valves V_(O),V_(INC), V_(INSS), E₁, E₂ of the valve block 3.

A fifth table 750 is shown in FIG. 12 to summarize, again for each ofthe valves V_(O), V_(INC), V_(INSS), E₁, E₂ of the valve block 3 (listedin the first columns of the first, second, third and fourth tables 710,720, 730, 740 described above), the number of valve cycles estimated ina time period of one year assuming different vehicle operationconditions (off road and on road) and different usage types (sand, wetgrass, mud and snow for the off road vehicle operation condition andeconomy (ECO), high speed, gross vehicle weight (GVW) and towing for theon road vehicle operating condition). Estimated valve cycles in one yearare also provided in FIG. 12 for a tire pressure maintenance condition(in the row before the last in the fifth table 750 shown in FIG. 12).The tire pressure maintenance condition relates to the pressuremaintaining strategy illustrated in FIG. 4. As can be seen from thefifth table 750, the valves V_(O), V_(INC), V_(INSS), E₁, E₂ of thevalve block 3 are estimated to collectively undergo 31,590 cycles in theunit time of one year.

FIGS. 13 to 16 show for parts of a per axle deflation cycle and a peraxle inflation cycle, the pressure measured in the gallery 33 by thepressure sensor 35 alongside the status of the various valves V, I, E ofthe valve block 3 illustrated in FIG. 1B.

A first graph 800 in FIG. 13 shows the pressure measured by the pressuresensor 35 during a first part of a tire deflation cycle identified overa time period from 151.5 sec (designated time t0) to 153.5 sec. At timet0, the pressure measured by the pressure sensor 35 is substantiallyequal to atmospheric pressure (Patm). This represents a stand-bycondition for the CTIS 1. At this time, the pressure at the pressuresensor 35 is representative of the pressure in the relevant tire supplylines TSL. At time t0, the measured pressure is equal to Patm since theexhaust valves E₁, E₂ are open, as illustrated by an eighth graph 835 inFIG. 13. At time t1 (152 sec), the rear outlet valves V_(RL), V_(RRO)are opened in preparation for deflating the tires of the rear axleT_(RL), T_(RR) of the vehicle VH, as shown in a fourth and fifth graph815, 820 in FIG. 13. The front outlet valves V_(FLO), V_(FRO) remainclosed throughout the time period represented in FIG. 13, as illustratedby a second and third graph 805, 810 in FIG. 13. At time t2(approximately 152.2 sec), the exhaust valves E₁, E₂ are closed therebysealing the tire supply lines TSL from atmosphere, as shown by theeighth graph 835. At time t2, the inlet valve V_(INSS) is instead openedto allow compressed air from the second compressed air source 7 into thetire supply lines TSL, as shown by a sixth graph 825 in FIG. 13. At timet2, therefore, the pressure sensor 35 detects a pressure increase in thegallery 33 of the valve block 3 as shown in the first graph 800. Theincoming compressed air from the second compressed air source 7 togglesthe pneumatic control valves located on the rear wheels PCV_(RL),PCV_(RR) to an open state. This is possible because the rear outletvalves V_(RLO), V_(RRO) are open at time t2. The instant at which therear pneumatic control valves PCV_(RL), PCV_(RR) are opened is time t3(approximately 152.4 sec) in FIG. 13. At time t3, the pressure sensor 35detects a dip in the pressure measured in the tire supply lines TSL. Fora short time period between time t3 and time t4 (approximately 152.6sec), pressure within the tires, the gallery and the tire supply linesequalizes resulting in a pressure fluctuation being seen at the pressuresensor. At time t5, the exhaust valves E₁, E₂ are opened and the secondinlet valve V_(INSS) is closed. These events initiate tire deflation.From time t5 onwards, compressed air flows from inside the rear tirecavities through the rear tire supply lines TSL_(RL), TSL_(RR) out toatmosphere. Thereafter, the pressure sensor 35 senses a pressure justabove atmospheric pressure Patm due to the incoming flow of compressedair from the rear tire cavities, as shown by the first graph 800 in FIG.13. It will be appreciated that during the tire deflation procedure, asshown by a seventh graph 830 in FIG. 13, the first compressed air source5 does not operate. Accordingly, the first inlet valve V_(INC) remainsclosed for the time period illustrated in FIG. 13.

In the described tire deflation procedure, compressed air flows from therear tire cavities out to atmosphere for a different deflation time foreach of the rear tires T_(RL), T_(RR). This deflation occurs over a timeperiod of approximately 100 seconds for the rear right tire T_(RR). Inparticular, the deflation of the rear right tire T_(RR) commences attime t5 (152.5 sec) when the exhaust valves E₁, E₂ open, as shown inFIG. 13. The deflation of the rear right tire T_(RR) ends at time t6(255.2 sec) when the rear right outlet valve V_(RRO) is closed, as shownin FIG. 14. As explained above, the deflation period is retrieved by theECU 15 on the basis of a look-up table stored in a memory. The look-uptable correlates pressure decrease with deflation time for the tiredeflation procedure, and pressure increase with inflation time for thetire inflation procedure. The rear left outlet valve V_(RLO) is closedat an intermediate time which is not shown in FIGS. 13 and 14. FIG. 14only relates to the rear axle tire measurement and closure proceduresstarting from time t8.

Referring now to FIG. 14, a first graph 840 of FIG. 14 shows thepressure measured by the pressure sensor 35 during a part of a tiredeflation cycle identified between a time period extending from 255 secto 259 sec. As shown by the first graph 840 in FIG. 14, the pressuremeasured by the pressure sensor 35 is substantially equal to theatmospheric pressure (Patm) since the rear right tire T_(RR) is deflateduntil time t6 (approximately 255.3 sec) and the exhaust valves E₁, E₂are open, as illustrated by an eighth graph 875 in FIG. 14. At time t6,the rear right outlet valve V_(RRO) is closed and, therefore, both therear tires T_(RL), T_(RR) are now ready to undergo the tire pressuremeasurement and pneumatic control valve closure procedures. For the rearleft tire T_(RL), this procedure begins at time t7 (just after 255.5sec), as shown in FIG. 14, with the opening of the rear left outletvalve T_(RL) as shown by a fourth graph 855 in FIG. 14. At time t8(approximately 255.7 sec), the exhaust valves E₁, E₂ are closed so thatthe pressure sensor 35 can now detect a tire pressure representative ofthe tire pressure in the rear left tire T_(RL). As soon as the exhaustvalves E₁, E₂ are closed, the pressure sensed by the pressure sensor 35starts to increase until it reaches the pressure representative of thetire pressure in the rear left tire T_(RL). The ECU 15 causes thepressure sensor 35 to take a reading at time t9 (approximately 256.3sec). Once the reading has been taken, the second inlet valve V_(INSS)is opened at t10 (256.5 sec) and closed at t11 (256.7 sec). Thisoperation, as explained above, toggles the rear left pneumatic controlvalve PCV_(RL) to a closed state and causes the pressure sensor 35 todetect pressures of up to about 9 bar, as shown by the first graph 840of FIG. 14. When the rear left pneumatic control valve PCV_(RL) islatched and the exhaust valves E₁, E₂ are opened at time t11 (256.7sec), the pressure sensed by the pressure sensor 35 is atmosphericpressure Patm again, which, as explained above, corresponds to astand-by condition. The first compressed air source 5 is not involved inthis procedure, as shown by a seventh graph 870 in FIG. 14 showing thefirst (i.e. HF/LP) inlet valve V_(INC) permanently closed. The frontoutlet valves V_(FLO), V_(FRO) are also not involved in the procedure,as shown by a second and third graph 845, 850 in FIG. 14. The tirepressure measurement and pneumatic control valve closure procedures arethen repeated for the rear right tire T_(RR) by nearly simultaneouslyclosing the rear left outlet valve V_(RLO) (as shown by the fourth graph855 of FIG. 14 at around time t12 (approximately 257.1 sec) and openingthe rear right outlet valve V_(RRO), as shown by a fifth graph 860 att13 (257.3 sec). At time t14 (257.5 sec), the exhaust valves E₁, E₂ areclosed and the pressure sensed by the pressure sensor 35 increases ascompressed air from the rear right deflated tire cavity populates thecorresponding tire supply line TSL_(RR). The ECU 15 causes a reading tobe taken from the pressure sensor 35 at time t15 (258 sec), as shown inthe first graph 840 in FIG. 14, when the pressure measured by thepressure sensor 35 is representative of the tire pressure in the rearright tire cavity. Between time t16 and time t17 the second inlet valveV_(INSS) (i.e. the LF/HP inlet valve) is opened and closed, which causesthe rear right pneumatic control valve PCV_(RR) to be closed. At timet17 (258.4 sec), the exhaust valves E₁, E₂ are opened to allow thecompressed air in the tire supply line TSL to be vented to atmosphere.At time t18 (approximately 258.8 sec), the pressure sensor 35 detects apressure equal to Patm, and therefore the system can return to stand-byat time t18. The rear tires T_(RL), T_(RR) have now been deflated to thetarget pressure of approximately 2.5 bar sensed, which corresponds to1.5 bar gauge.

Referring now to FIG. 15, a first graph 880 in FIG. 15 shows thepressure measured by the pressure sensor 35 during a preparatory part ofa tire inflation cycle from an initial time t′0 (303.5 sec). At t′1(304.3 sec), the ECU 15 causes the first compressed air source 5 todeliver compressed air by opening the inlet valve V_(INC), as shown by aseventh graph 910 in FIG. 15. Pressure starts to build up in the gallery33 of the valve block 3. At time t′2 (304.5 sec), the rear outlet valvesV_(RLO), V_(RRO) are opened by the ECU 15, as shown by a fourth and afifth graph 895, 900 in FIG. 15. Compressed air from the compressor 9can therefore flow into the tire supply lines TSL_(RL), TSL_(RR)relating to the rear axle of the vehicle VH. A dip in the measuredpressure is sensed by the pressure sensor 35 at t′3 (304.6 sec) as aconsequence of this flow of compressed air into the rear tire supplylines TSL_(RL), TSL_(RR). Subsequently, the pressure sensed by thepressure sensor 35 increases again due to additional compressed airinput to the rear tire supply lines TSL_(RL), TSL_(RR) by the compressor9. The system is now ready for inflating the rear tires T_(RL), T_(RR).The front outlet valves V_(FLO), V_(FRO) are not involved in thisprocedure (i.e. these valves remain closed), as shown by a second and athird graph 885, 890 in FIG. 15. Likewise, the second (denoted LF/HP inFIG. 15) inlet valve V_(INSS) and the exhaust valves E₁, E₂ are notinvolved, as shown by respectively a sixth and an eighth graph 905, 915in FIG. 15.

Inflation is achieved by opening and closing the second inlet valveV_(INSS) (i.e. the LF/HP valve) so as to toggle the rear left and rearright pneumatic control valves PCV_(RL), PCV_(RR) to an open state (thisis not shown in FIG. 15 or 16). Compressed air can thus flow from thefirst compressed air source 5 to the relevant tire cavities for apredetermined time period. The pressure sensor 35 senses the pressure ofthe compressed air supplied from the first compressed air source 5. Asdescribed herein, the target tire pressure is achieved by controllingthe inflation time. The tire inflation ends for the rear left tireT_(RL) at a time not shown in FIGS. 15 and 16.

Referring now to FIG. 16, the tire inflation ends for the rear righttire T_(RR) at time t′4 (323.7 sec) shown in FIG. 16, when the rearright outlet valve V_(RRO) is closed as shown by a fifth graph 940 inFIG. 16. The system is then reconfigured to measure the pressure in therear left tire cavity. This procedure starts in FIG. 16 at time t′5(232.8 sec), when the first inlet valve V_(INC) (denoted HF/LP valve inFIG. 16) is closed (thereby cutting out flow of compressed air from thecompressor 9) as shown by a seventh graph 950 in FIG. 16, and theexhaust valves E1, E2 are opened to vent out excess compressed air fromthe relevant tire supply lines TSL_(RR), TSL_(RL) as shown by an eighthgraph 955 in FIG. 16. At time t′6 (323.9 sec), the rear left outletvalve V_(RLO) is opened to put the rear left tire supply line TSL_(RL)in communication with the inflated rear left tire cavity, as shown by afourth graph 935 in FIG. 16. Soon after time t′7 (234.2 sec), theexhaust valves E₁, E₂ are closed to prevent air from the rear left tireT_(RL) from venting out thereby deflating the previously inflated rearleft tire T_(RL). The rear left tire supply line TSL_(RL) fills withcompressed air. The pressure in the rear left tire supply line TSL_(RL)is now representative of the pressure in the rear left tire T_(RL) whichcan thus be estimated via the pressure measured by the pressure sensor35 in the gallery 33 of the valve block 3 at time t′8 (324.7 sec), asshown by a first graph 920 in FIG. 16. If the pressure achieved iscorrect, the second inlet valve V_(INSS) (denoted LF/HP in FIG. 16) canbe opened and closed to isolate the rear left tire cavity. This happensin FIG. 16 between time t′9 (324.9 sec) and time t′10 (325.2 sec), asshown by a sixth graph 945 in FIG. 16. This procedure closes the rearleft pneumatic control valve PCV_(RL) to isolate the rear left tirecavity. At time t′10, the exhaust valves E₁, E₂ are also opened to ventout excess air from the rear left tire supply line TSL_(RL). Since thetarget pressure (2.5 bar) has been reached, the procedure can beterminated for the rear left tire T_(RL). This happens, in FIG. 16, att′11 (325.5 sec) when the rear left outlet valve V_(RLO) is closed. Theprocedure is then repeated for the rear right tire T_(RR). The frontoutlet valves V_(FLO), V_(FRO) are not involved in this procedure (i.e.they remain permanently closed), as shown by a second and a third graph925, 930 in FIG. 16. At time t′12 (325.7 sec), the rear right outletvalve V_(RRO) is opened and at time t′13 (325.9 sec) the exhaust valvesE₁, E₂ are closed to isolate the rear right tire supply line TSL_(RR) sothat the rear right tire pressure can be measured. The measurement istaken by the pressure sensor 35 at time t′14 (326.4 sec). The secondinlet valve V_(INSS) is then opened and closed at times t′15 (326.7 sec)and t′16 (329.9 sec) respectively to operate the rear right pneumaticcontrol valve PCV_(RL) to seal the rear right tire cavity. At time t′16,the exhaust valves E₁, E₂ are also opened to vent excess compressed airfrom the rear right tire supply line TSL_(RR). At time t′17 (237.3 sec)approximately, the rear right outlet valve V_(RR) and the exhaust valvesE₁, E₂ are closed to terminate the procedure.

An additional control strategy implemented by the CTIS 1 describedherein is described below. This control strategy relates to a targettire pressure over-shooting strategy.

Over the life of the vehicle VH, the various joints in the compressedair paths between the compressed air sources and the tire cavities inthe CTIS 1 may develop minor leaks due to normal, ageing wear. As aconsequence, during a tire inflation or deflation operation the CTIS 1may, respectively, undershoot or overshoot the target tire pressures.This is due to the presence of such leaks, or losses, whereby during atire inflation operation some of compressed air destined to the tirecavities is instead vented from the CTIS 1 to atmosphere due to one ormore leaks. During a tire deflation operation, an additional quantity ofcompressed air may vent from the CTIS 1 to atmosphere due to thesepotential leaks.

Since the CTIS 1 described herein is based on an open loop systemarchitecture (i.e. there is no feedback means to feedback to the ECU 15the amount of compressed air being actually or instantaneouslytransferred to the tire cavities as the tires are inflated or beingactually or instantaneously vented to atmosphere as the tires aredeflated), a tire inflation or deflation operation is terminated after agiven/predetermined tire inflation or deflation time has elapsed. Asdescribed earlier, these given/predetermined times are retrieved by theECU 15 from the look-up table. Subsequently, the tire pressures aremeasured for each of the tires T involved in the inflation or deflationprocedures to check whether the tire inflation or deflation hasdelivered the target tire pressures. In this open loop system, the ECU15 is only programmed to check that the inflation or deflation time isequivalent to the inflation or deflation time retrieved from memory andto successively verify the tire pressure and close the pneumatic controlvalves PCV by activating respectively the pressure measurement procedureand the pneumatic control valve closure procedure as described herein.These events terminate the overall tire inflation or deflationcycle/procedure.

In both scenarios (tire inflation or deflation), it is undesirable tohave to inflate the tires further in a subsequent step to reach thetarget tire pressures, since this would require at least anotherinflation or deflation cycle (i.e. inclusive of the tire pressuremeasurement and pneumatic control valve closure operations). A furthertire inflation cycle is especially undesirable since it could require afurther activation of the compressor 9 via the electric motor 27 withrelated noise. Further, any additional inflation or deflationcycle/procedure equates to additional energy consumed, potentialadditional noise emitted by the CTIS 1, additional time required toreach the target pressures, additional valve cycles for one or more ofthe various valves of the CTIS 1 and, in particular, the pneumaticcontrol valves PCV. Once the tire pressures have been measured afterinflation or deflation the system is required to cycle through thepneumatic valve closure procedure before the valves can be brought backto the tire inflation configuration. Then the pneumatic control valvesPCV are required to cycle again through the pressure check/measurementconfiguration before the pneumatic control valves PCV can beclosed/latched to terminate the inflation or deflation cycles/proceduresas earlier described. An additional problem is that if the requiredadditional inflation time is particularly short, initialization of thecompressor 9 and the air dryer unit 29 may be problematic and the CTIS 1may consequently generate a system fault as illustrated by System Faultstatus 25 illustrated in FIG. 2.

In the described embodiment, the ECU 15 of the CTIS 1 is programmed toprovide compensation to try to address the aforementioned problem. Inparticular, the ECU 15 is programmed to ensure that at the end of theinflation or deflation operations (identified by flow of compressed airto or from one or more tires T) the tire pressures are each greater thanthe target tire pressures. In other words, the ECU 15 is programmed soas always to include a safety overshooting or compensation margin at theend of the inflation or deflation operations/times. As a consequence,the ECU 15 is programmed to overshoot the target tire pressure in thecase of tire inflation and to undershoot the target tire pressure in thecase of tire deflation. The overshooting tire pressure (or compensationtire pressure) corresponds to the target tire pressure plus a margin.

In an example, the ECU 15 retrieves from the look-up table an inflationtime equal to 60 sec and adds a safety margin of 6 sec to overshoot thetarget tire pressure thereby inflating above the target tire pressure.In another example, the ECU 15 retrieves from memory a deflation time of100 sec and subtracts a safety margin of 15 sec to undershoot the targettire pressure thereby under-deflating the relevant tire T. Once thetarget tire pressure have been overshot or undershot by the CTIS 1 so asto avoid further one or more full tire inflation/deflation cycles, theECU 15 is programmed to adjust the target tire pressure during thefollowing Measure procedure 515 (examples of which as shown in FIGS. 5to 7) to adjust the tire pressure to the target pressure. During theMeasure procedure 515, the CTIS 1 can adjust the tire pressure asrequired by simply opening the exhaust valves E₁, E₂ until the targettire pressure has been achieved. The CTIS 1 is therefore no longerrequired to undertake one or more additional inflation cycles.

Criteria can be developed to estimate, or calculate, the safety margin(also referred to herein as the over-shooting margin or the compensationmargin). In particular, it would be preferable to be able to estimate orcalculate safety margins which allow the system to overshoot (in thecase of tire inflation) or undershoot (in the case of tire deflation)the target tire pressure as little as possible while at the same timeresulting into inflation above or slightly above the target tirepressure at the end of the inflation or deflation operation/time. Insome embodiments, the over-shooting margin is established on the basisof a worst-case scenario which is associated to a maximum of compressedair loss through the joints. In this case, the safety margin equals tothe additional inflation time, or to the subtracted deflation time, asthe case may be, which is required to compensate for the maximum ofcompressed air loss associated with the worst-case scenario. As it willbe understood, a variety of worst-case scenarios could be hypothesizedand, accordingly, a range of maximum losses could be used. For example,the worst case scenario may be estimated based on the possible number ofpoints at which a leak may occur and the estimated maximum leak at eachlocation. Empirical testing may be used to obtain data from which toestimate the maximum leak at each location. In order to determine thecondition of the seals the safety margin may use a worst case scenarioof the expected air leakage after a predetermined usage, for exampleafter 100,000 miles. If, using this valve, prior to the vehicle reaching100,000 miles usage, after the first part of the inflation the pressureis below the target pressure, this may be indicative of significant sealdeterioration outside of expected parameters and a notification may beissued to the driver, for example through a vehicle HMI.

The compensation margin could be calculated as the additional inflationtime, or to the subtracted deflation time, as the case may be, which isrequired to compensate for the maximum loss of compressed air lossthrough one or more of the rotary air couplings VH.

It is also predicted that the aforementioned compressed air losses maydepend on vehicle age or mileage. Accordingly, the over-shooting margincould be dependent on, or be a function of, vehicle age or mileage.

It is also conceivable to use the CTIS 1 to measure the air loss, or airloss rates, through the joints at one or more times throughout the lifeof the vehicle. In this case, the CTIS 1 is configured to convert ameasured discrepancy between the target tire pressure and the currenttire pressure for one or more of the tires following a tire inflation ordeflation procedure into an estimated air loss or air loss rate. Inparticular, the CTIS 1 could be configured to individually test therotary air couplings RAC in this manner to estimate the air loss, or airloss rate, through each of the rotary air couplings RAC at one or moretimes. The resulting compensation margins could then be applied to thetires individually, or for each axle, if appropriate. Alternatively, theoutlet valves V_(O) may be opened, the PCV valves closed, the exhaustvalves E₁, E₂ closed, and pressure applied by opening and closing thefirst inlet valve V_(INC) to pressurize the air-path to the tire. Thepressure sensed at the pressure sensor 35 can then be observed and anyreduction can be assumed to be as a result of system leakage lossesbetween the valve block 3 and the pneumatic control valves PCV. Theoutlet valves V_(O) may be individually opened to estimate the losses inthe air path to each tire T.

It is also conceivable to use combinations of the above describedcriteria or methodologies for the calculation or estimation of thecompensation margin or margins, or to refine the above describedcriteria or methodologies in various manners which are however notdescribed herein in detail.

1. A central tire inflation system for a vehicle comprising: at leastone pneumatic control valve for controlling inflation of a respectivetire; a first compressed air source for supplying compressed air toinflate the tire; a second compressed air source for supplyingcompressed air at a higher pressure than the first compressed air sourceto control said at least one pneumatic control valve; and control meansfor controlling the supply of compressed air from the second compressedair source to generate a pneumatic control signal comprising a pulse ofair to control said at least one pneumatic control valve; wherein the atleast one pneumatic control valve is a latching valve having a pluralityof operating states and the at least one pneumatic control valve isoperative to toggle between operating states, or to cycle throughoperating states in dependence on the pneumatic control signal.
 2. Acentral tire inflation system as claimed in claim 1, wherein the secondcompressed air source comprises a compressed air reservoir of an airsuspension system.
 3. (canceled)
 4. A central tire inflation system asclaimed in claim 1, wherein the first compressed air source suppliescompressed air at a higher flow rate than the second compressed airsource.
 5. A central tire inflation system as claimed in claim 1comprising a first inlet valve for controlling the supply of compressedair from the first compressed air source.
 6. A central tire inflationsystem as claimed in claim 5, wherein the control means comprises asecond inlet valve for controlling the supply of compressed air from thesecond compressed air source.
 7. A central tire inflation system asclaimed in claim 6, wherein the control means comprises a controller forcontrolling operation of the second inlet valve to generate saidpneumatic control signal.
 8. A central tire inflation system as claimedin claim 6, wherein the first and second inlet valves control the supplyof compressed air from the respective first and second compressed airsources to a fluid gallery.
 9. A central tire inflation system asclaimed in claim 8 comprising an outlet valve for controlling the supplyof compressed air from the fluid gallery to a tire supply line.
 10. Acentral tire inflation system as claimed in claim 9, wherein the tiresupply line is in fluid communication with the pneumatic control valve.11. A central tire inflation system as claimed in claim 10, wherein thetire supply line is operative to supply compressed air from said firstcompressed air source and/or from said second compressed air source. 12.A central tire inflation system as claimed in claim 10 comprising aplurality of said pneumatic control valves each for controlling a flowof compressed air to a respective tire of the vehicle, wherein eachpneumatic control valve is operably coupled to a respective tire supplyline and a respective outlet valve.
 13. A central tire inflation systemas claimed in claim 12, wherein, in use, more than one of said pluralityof pneumatic control valves can be controlled simultaneously by the samepneumatic control signal.
 14. (canceled)
 15. A method of operating acentral tire inflation system to inflate a tire of a vehicle, the methodcomprising the steps of: using a first compressed air source, providinga first supply of compressed air for inflating the tire; using a secondcompressed air source for supplying compressed air at a higher pressurethan the first compressed air source, generating a pneumatic controlsignal comprising a pulse of air to control operation of a pneumaticcontrol valve for controlling inflation of the tire, the pneumaticcontrol valve being a latching valve having a plurality of operatingstates and being operative to toggle between operating states, or tocycle through operating states in dependence on the pneumatic controlsignal.
 16. A computer program product comprising a non-transitorycomputer readable storage medium including computer readable programcode, wherein the computer readable program code when executed causes acentral tire inflation system to inflate a tire of a vehicle accordingto the method of claim
 15. 17. A vehicle comprising a central tireinflation system as claimed in claim
 1. 18-19. (canceled)